U.S. summer nuclear outages rose in 2023, returning to 2021 levels

Outages of U.S. nuclear generating capacity averaged 3.1 gigawatts (GW) per day during the summer of 2023 (June 1 through August 31), a return to 2021 levels. Capacity outages this past summer exceeded those in summer 2022 by more than 25%. Nuclear capacity outages peaked in June because some reactors were still offline at the end of the spring refueling and maintenance season. June capacity outages averaged 6.1 GW per day and peaked at 8.3 GW.

Nuclear power plants undergo both planned outages, usually for maintenance and refueling, and unplanned outages, which include weather-related disruptions and early retirements. The fewest nuclear outages usually occur in the United States during the summer and winter because electricity demand is highest during these seasons and plant operators need to have reactors available to meet increased seasonal electricity demand.

Planned nuclear generation outages are usually scheduled to coincide with reactor refueling cycles. U.S. nuclear power plants typically refuel reactors every 18 to 24 months, mostly in fall and spring when electricity demand is lower. During a refueling outage, plants typically optimize downtime by scheduling facility upgrades, repairs, and other maintenance work while the nuclear reactor is offline.

As of October 3, 2023, U.S. nuclear plant refueling outages this year have averaged 35 days compared with 38 days during 2022. Several reactors began refueling and maintenance outages in April and May and were offline for an average of 34 days. Some reactors were offline for much longer than average: Millstone Nuclear Plant in Waterford, Connecticut, was offline for 89 days, and the Columbia Generating Station in Richland, Washington, began a 44-day outage in early May. Both outages lasted into June and increased the overall summer capacity outage duration.

Unplanned, or forced, nuclear generation outages can result from equipment failure, operational error, or external circumstances such as severe weather. As of October 3, the United States had 31 unplanned U.S. nuclear outages in 2023, compared with 35 in 2022.

The Fermi Nuclear Generating Station, located about 30 miles south of Detroit, was shut down from August 21 to September 7 after operators detected a coolant leak. The facility underwent a 54-day planned outage in early 2022 when about one-third of the fuel in the reactor was replaced and maintenance and testing activities were conducted throughout.

Vogtle Unit 3 in Waynesboro, Georgia, shut down for three days in mid-July for an unplanned maintenance outage and hot weather alert. The reactor entered commercial operation two weeks later on July 31.

Our Status of Nuclear Outages web page, which is based on data collected by the U.S. Nuclear Regulatory Commission, provides daily operational information on each commercial U.S. nuclear power reactor.